A retrospective cohort study on the influence of UV index and race/ethnicity on risk of stress and lower limb fractures

Current risks factors and emerging biomarkers for bone stress injuries in military personnel

INTRODUCTION

Bone stress injuries (BSIs) have plagued the military for over 150 years; they afflict around 5 to 10% of military recruits, more so in women, and continue to place a medical and financial burden on defence. While the tibia generally adapts to the rigours of basic military training, the putative mechanisms for bone maladaptation are still unclear.

METHODS

This paper provides a review of the published literature on current risk factors and emerging biomarkers for BSIs in military personnel; the potential for biochemical markers of bone metabolism to monitor the response to military training; and, the association of novel biochemical 'exerkines' with bone health.

RESULTS

The primary risk factor for BSI in military (and athletic) populations is too much training, too soon. Appropriate physical preparation before training will likely be most protective, but routine biomarkers will not yet identify those at risk. Nutritional interventions will support a bone anabolic response to training, but exposure to stress, sleep loss, and medication is likely harmful to bone. Monitoring physiology using wearables-ovulation, sleep and stress-offer potential to inform prevention strategies.

CONCLUSIONS

The risk factors for BSIs are well described, but their aetiology is very complex particularly in the multi-stressor military environment. Our understanding of the skeletal responses to military training is improving as technology advances, and potential biomarkers are constantly emerging, but sophisticated and integrated approaches to prevention of BSI are warranted.

Femoral Neck Stress Fractures in Athletes and the Military

➤

Femoral neck stress fractures (FNSFs) are an infrequent condition in athletic and military populations.

➤

A high index of suspicion with liberal use of magnetic resonance imaging (MRI) is vital for early recognition and treatment initiation.

➤

An associated hip effusion on MRI is a risk factor for an evolving stress injury and requires close assessment and consideration for repeat MRI.

➤

Stress reactions and stable, incomplete FNSFs (<50% of femoral neck width) can be treated nonsurgically.

➤

Surgical intervention is accepted for high-risk, incomplete (≥50% of femoral neck width), and complete FNSFs.

➤

Overall, there is a paucity of high-quality literature on the rates of return to activity following FNSF.

Risk factors for musculoskeletal injuries in the military: a qualitative systematic review of the literature from the past two decades and a new prioritizing injury model

BACKGROUND

Musculoskeletal injuries (MSkIs) are a leading cause of health care utilization, as well as limited duty and disability in the US military and other armed forces. MSkIs affect members of the military during initial training, operational training, and deployment and have a direct negative impact on overall troop readiness. Currently, a systematic overview of all risk factors for MSkIs in the military is not available.

METHODS

A systematic literature search was carried out using the PubMed, Ovid/Medline, and Web of Science databases from January 1, 2000 to September 10, 2019. Additionally, a reference list scan was performed (using the "snowball method"). Thereafter, an international, multidisciplinary expert panel scored the level of evidence per risk factor, and a classification of modifiable/non-modifiable was made.

RESULTS

In total, 176 original papers and 3 meta-analyses were included in the review. A list of 57 reported potential risk factors was formed. For 21 risk factors, the level of evidence was considered moderate or strong. Based on this literature review and an in-depth analysis, the expert panel developed a model to display the most relevant risk factors identified, introducing the idea of the "order of importance" and including concepts that are modifiable/non-modifiable, as well as extrinsic/intrinsic risk factors.

CONCLUSIONS

This is the qualitative systematic review of studies on risk factors for MSkIs in the military that has attempted to be all-inclusive. A total of 57 different potential risk factors were identified, and a new, prioritizing injury model was developed. This model may help us to understand risk factors that can be addressed, and in which order they should be prioritized when planning intervention strategies within military groups.

Musculoskeletal Injuries Among Females in the Military: A Scoping Review

INTRODUCTION

Musculoskeletal injuries (MSKi) are a common challenge for those in military careers. Compared to their male peers, reports indicate that female military members and recruits are at greater risk of suffering MSKi during training and deployment. The objectives of this study were to identify the types and causes of MSKi among female military personnel and to explore the various risk factors associated with MSKi.

MATERIALS AND METHODS

A scoping review was conducted over a 4-month time frame of English language, peer-reviewed studies published from 1946 to 2019. Search strategies for major biomedical databases (e.g., MEDLINE; Embase Classic + Embase; and the following EBM Reviews-Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews, Database of Abstracts of Reviews of Effects, Health Technology Assessment, and the NHS Economic Evaluation Database) were developed by a senior medical information specialist and included 2,891 titles/abstracts. Study selection and data collection were designed according to the Population, Concept, and Context framework. Studies were included if the study population provided stratified data for females in a military context.

RESULTS

From a total of 2,287 citations captured from the literature searches, 168 peer-reviewed publications (144 unique studies) were eligible for inclusion. Studies were identified from across 10 countries and published between 1977 and 2019. Study designs were primarily prospective and retrospective cohorts. Most studies assessed both prevalence/incidence and risk factors for MSKi (62.50%), with few studies assessing cause (13.69%). For MSKi of female recruits compared to active female members, the prevalence was higher (19.7%-58.3% vs. 5.5%-56.6%), but the incidence (0.02%-57.7% vs. 13.5%-71.9%) was lower. The incidence of stress fractures was found to be much higher in female recruits than in active members (1.6%-23.9% vs. 2.7%). For anthropometric risk factors, increased body fat was a predictor of MSKi, but not stress fractures. For physiological risk factors for both female military groups, being less physically fit, later menarche, and having no/irregular menses were predictors of MSKi and stress fractures. For biomechanical risk factors, among female recruits, longer tibial length and femoral neck diameter increased the risk of stress fractures, and low foot arch increased risk of an ankle sprain. For female active military members, differences in shoulder rotation and bone strength were associated with risk of MSKi. For biological sex, being female compared to male was associated with an increased risk of MSKi, stress fractures, and general injuries. The consequences of experiencing MSKi for active military included limited duties, time off, and discharge. For recruits, these included missed training days, limited duty days, and release.

CONCLUSIONS

This scoping review provides insight into the current state of the evidence regarding the types and causes of MSKi, as well as the factors that influence MSKi among females in the military. Future research endeavors should focus on randomized controlled trials examining training paradigms to see if women are more susceptible. The data presented in the scoping review could potentially be used to develop training strategies to mitigate some of the identified barriers that negatively impact women from pursuing careers in the military.

Timing of stress fracture in soldiers during the first 6 career months: a retrospective cohort study

CONTEXT

Stress fractures (SF) are injuries that can result from beginning new or higher volume physical training regimens. The pattern of clinical presentation of SF over time after individuals start a new or more demanding physical training regimen is not well defined in medical literature.

OBJECTIVE

Report trends in the clinical presentation of stress fractures over the first six month of soldiers' time in the service.

DESIGN

Retrospective Cohort study Setting: This study was conducted using medical encounter and personnel data from U.S. Army soldiers during the first 6 months of their career.

PARTICIPANTS

U.S. Army soldiers beginning their careers from 2005-2014 (N=701,027).

DATA COLLECTION AND ANALYSIS

Weekly SF numbers and incidence were calculated overall, as well as by sex, over the first 6 months of military service.

RESULTS

SF diagnoses (N=14,155) increased steeply in weeks 3 and 4, with a peak in the overall incidence of SF diagnoses occurring during weeks 5-8. Although clinical incidence of stress fracture generally decreased beyond 8 weeks, incident lower extremity stress fractures continued to present for over 20 weeks. The hazard ratio (HR) for SF among women compared to men was 4.14 (95% CI = [4.01, 4.27]).

CONCLUSIONS

Across the 6-month study period, women showed over 4 times greater hazard for stress fracture. The results also suggest that health care providers should be particularly vigilant for stress fractures within 3 weeks after the beginning of a new or higher intensity exercise regimen. The incidence of SF may continue to climb for several weeks. Even as stress fracture incidence declines, it should be noted that these injuries may also continue to appear clinically even several months after a change in activity or training.

Markers of Bone Health and Impact of Whey Protein Supplementation in Army Initial Entry Training Soldiers: A Double-Blind Placebo-Controlled Study

Training civilians to be soldiers is a challenging task often resulting in musculoskeletal injuries, especially bone stress injuries. This study evaluated bone health biomarkers (P1NP/CTX) and whey protein or carbohydrate supplementations before and after Army initial entry training (IET). Ninety male IET soldiers participated in this placebo-controlled, double-blind study assessing carbohydrate and whey protein supplementations. Age and fat mass predicted bone formation when controlling for ethnicity, explaining 44% (p < 0.01) of bone formation variations. Age was the only significant predictor of bone resorption (p = 0.02) when controlling for run, fat, and ethnicity, and these factors together explained 32% of the variance in bone resorption during week one (p < 0.01). Vitamin D increased across training (p < 0.01). There was no group by time interaction for supplementation and bone formation (p = 0.75), resorption (p = 0.73), Vitamin D (p = 0.36), or calcium (p = 0.64), indicating no influence of a supplementation on bone biomarkers across training. Age, fitness, fat mass, and ethnicity were important predictors of bone metabolism. The bone resorption/formation ratio suggests IET soldiers are at risk of stress injuries. Male IET soldiers are mildly to moderately deficient in vitamin D and slightly deficient in calcium throughout training. Whey protein or carbohydrate supplementations did not affect the markers of bone metabolism.

A prospective field study of U.S. Army trainees to identify the physiological bases and key factors influencing musculoskeletal injuries: a study protocol

BACKGROUND

Musculoskeletal injuries (MSKIs) are common in military trainees and present a considerable threat to occupational fitness, deployability, and overall military readiness. Despite the negative effects of MSKIs on military readiness, comprehensive evaluations of the key known and possible risk factors for MSKIs are lacking. The U.S. Army Research Institute of Environmental Medicine (ARIEM) is initiating a large-scale research effort, the ARIEM Reduction in Musculoskeletal Injury (ARMI) Study, to better understand the interrelationships among a wide range of potential MSKI risk factors in U.S. Army trainees in order to identify those risk factors that most contribute to MSKI and may be best targeted for effective mitigation strategies.

METHODS

This prospective study aims to enroll approximately 4000 (2000 male and 2000 female) U.S. Army trainees undergoing Basic Combat Training (BCT). Comprehensive in-person assessments will be completed at both the beginning and end of BCT. Participants will be asked to complete surveys of personal background information, medical history, physical activity, sleep behaviors, and personality traits. Physical measurements will be performed to assess anthropometrics, tibial microarchitecture and whole body bone mineral density, muscle cross-sectional area, body composition, and muscle function. Blood sampling will be also be conducted to assess musculoskeletal, genetic, and nutritional biomarkers of risk. In addition, participants will complete weekly surveys during BCT that examine MSKI events, lost training time, and discrete risk factors for injury. Participants' medical records will be tracked for the 2 years following graduation from training to identify MSKI events and related information. Research hypotheses focus on the development of a multivariate prediction model for MSKI.

DISCUSSION

Results from this study are expected to inform current understanding of known and potential risk factors for MSKIs that can be incorporated into solutions that optimize Soldier health and enhance military readiness.

Development of a Prediction Model for Stress Fracture During an Intensive Physical Training Program: The Royal Marines Commandos

BACKGROUND

Stress fractures (SFs) are one of the more severe overuse injuries in military training, and therefore, knowledge of potential risk factors is needed to assist in developing mitigating strategies.

PURPOSE

To develop a prediction model for risk of SF in Royal Marines (RM) recruits during an arduous military training program.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

RM recruits (N = 1082; age range, 16-33 years) who enrolled between September 2009 and July 2010 were prospectively followed through the 32-week RM training program. SF diagnosis was confirmed from a positive radiograph or magnetic resonance imaging scan. Potential risk factors assessed at week 1 included recruit characteristics, anthropometric assessment, dietary supplement use, lifestyle habits, fitness assessment, blood samples, 25(OH)D, bone strength as measured by heel broadband ultrasound attention, history of physical activity, and previous and current food intake. A logistic least absolute shrinkage and selection operator (LASSO) regression with 10-fold cross-validation was used to select potential predictors among 47 candidate variables. Model performance was assessed using measures of discrimination (c-index) and calibration. Bootstrapping was used for internal validation of the developed model and to quantify optimism.

RESULTS

A total of 86 (8%) volunteer recruits presented at least 1 SF during training. Twelve variables were identified as the most important risk factors of SF. Variables strongly associated with SF were age, body weight, pretraining weightbearing exercise, pretraining cycling, and childhood intake of milk and milk products. The c-index for the prediction model, which represents the model performance in future volunteers, was 0.73 (optimism-corrected c-index, 0.68). Although 25(OH)D and VO₂max had only a borderline statistically significant association with SF, the inclusion of these factors improved the performance of the model.

CONCLUSION

These findings will assist in identifying recruits at greater risk of SF during training and will support interventions to mitigate this injury risk. However, external validation of the model is still required.

Risk of Stress Fracture Varies by Race/Ethnic Origin in a Cohort Study of 1.3 Million US Army Soldiers

Stress fractures (SF) are common and costly injuries in military personnel. Risk for SF has been shown to vary with race/ethnicity. Previous studies report increased SF risk in white and Hispanic Soldiers compared with black Soldiers. However, these studies did not account for the large ethnic diversity in the US military. We aimed to identify differences in SF risk among racial/ethnic groups within the US Army. A retrospective cohort study was conducted using data from the Total Army Injury and Health Outcomes Database from 2001 until 2011. SF diagnoses were identified from ICD-9 codes. We used Cox-proportional hazard models to calculate time to SF by racial/ethnic group after adjusting for age, education, and body mass index. We performed a sex-stratified analysis to determine whether the ethnic variation in SF risk depends on sex. We identified 21,549 SF cases in 1,299,332 Soldiers (more than 5,228,525 person-years of risk), revealing an overall incidence rate of 4.12 per 1000 person-years (7.47 and 2.05 per 1000 person-years in women and men, respectively). Using non-Hispanic blacks as the referent group, non-Hispanic white women had the highest risk of SF, with a 92% higher risk of SF than non-Hispanic black women (1.92 [1.81-2.03]), followed by American Indian/Native Alaskan women (1.72 [1.44-1.79]), Hispanic women (1.65 [1.53-1.79]), and Asian women (1.32 [1.16-1.49]). Similarly, non-Hispanic white men had the highest risk of SF, with a 59% higher risk of SF than non-Hispanic black men (1.59 [1.50-1.68]), followed by Hispanic men (1.19 [1.10-1.29]). When examining the total US Army population, we found substantial differences in the risk of stress fracture among racial/ethnic groups, with non-Hispanic white Soldiers at greatest risk and Hispanic, American Indian/Native Alaskan, and Asian Soldiers at an intermediate risk. Additional studies are needed to determine the factors underlying these race- and ethnic-related differences in stress fracture risk. © 2017 American Society for Bone and Mineral Research.

Increasing ultraviolet light exposure is associated with reduced mortality from Clostridium difficile infection

BACKGROUND

Clostridium difficile infection (CDI) is an increasingly common cause of inpatient mortality. Vitamin D deficiency is associated with more aggressive CDI. We aimed to determine if average annual ultraviolet light (UV) exposure was associated with mortality in patients with CDI.

METHODS

We used the US National Inpatient Sample (NIS) from 2004-2011 to assess the mortality risk in patients with a diagnosis of CDI (as per ICD-9CM 008.45). Annual average state UV exposure was assigned to each hospitalization. Logistic regression was used to determine the effects of UV exposure on mortality, controlling for age, gender, race and other comorbidities.

RESULTS

During the study period, there were 2.61 million hospitalizations with a diagnosis of CDI. The mortality rate was 9.0%. In univariate analysis, the odds ratio (OR) of inpatient mortality for the UV index was 0.97 (95% CI 0.95-0.99; p = 0.008) per unit of UV exposure. In a multivariable model adjusting for age, gender, race, Charlson-Deyo index, season and coexisting inflammatory bowel disease, the UV index remained a protective predictor, with an OR of 0.94 (95% CI 0.92-0.96; p < 0.001). In the multivariate model, a seasonal effect was also present, with the highest risk of inpatient mortality in the period from January to March (OR 1.11; 95% CI 1.08-1.14) and the lowest risk, from July to September (OR 0.95; 95% CI 0.92-0.98).

CONCLUSIONS

An increase in UV exposure index is associated with a reduced risk of inpatient mortality in patients with CDI. A seasonal effect is also present, with the highest risk of death during winter months. Further studies exploring the role of UV light in CDI are necessary.

Increased ultraviolet light exposure is associated with reduced risk of inpatient surgery among patients with Crohn's disease

BACKGROUND AND AIMS

Due to the formation of strictures and fistulas, patients with Crohn's disease (CD) frequently need surgery. Vitamin D has been found to play a role in the degree of inflammation. We aimed to study the effect of UV exposure on the need for inpatient surgery in patients with CD.

METHODS

The national inpatient sample, the largest database of hospitalizations from the USA, was used to conduct a retrospective study of patients hospitalized from 2004-2011 with CD by ICD-9CM code 555. Surgery was characterized as any intestinal surgery or fistula repair. An average state UV exposure was calculated for each hospitalization. Multivariate logistic regression was used to calculate the effect of UV exposure on surgery accounting for important covariates.

RESULTS

There were 481712 hospitalizations with a primary diagnosis of CD. Of these hospitalizations, 67751 included a relevant surgical procedure code. Mean UV exposure was statistically lower in the group undergoing surgery (4.3 units versus 4.4 units, p = 0.001). The ratio of hospitalizations per UV exposure tertile for CD was statistically different compared with all hospitalizations (p < 0.001). In univariate analysis, increased UV exposure was associated with a lower risk of inpatient surgery with an OR of 0.90 per unit (95% CI 0.84-0.96, p = 0.001). Accounting for age, gender, race/ethnicity, season, income, hospital setting, and Charlson-Deyo comorbidities, the effect of UV exposure remained protective for inpatient surgery (OR 0.91, 95% CI: 0.84-0.98, p = 0.01).

CONCLUSIONS

Increased UV exposure is associated with a reduced risk of inpatient surgery among patients with CD. Further studies of vitamin D's role in CD are necessary.

Injury during U.S. Army basic combat training: a systematic review of risk factor studies

CONTEXT

Approximately one quarter of men and half of women in U.S. Army basic combat training experience an injury. Preventing basic combat training-related injuries would reduce associated human and economic costs and discharges from the Army. Identification of risk factors for such injuries is a crucial step toward their prevention. Although some research has begun to address this need, prior studies of risk factors for training-related injury have not been reviewed systematically. This study systematically reviews the literature on risk factors for injury during U.S. Army basic combat training.

EVIDENCE ACQUISITION

Original studies of risk factors for injury during U.S. Army basic combat training published since 1990 in peer-reviewed journals were identified using PubMed and manual searches of reference lists. This search was last performed in May 2013. Nineteen studies met the inclusion criteria.

EVIDENCE SYNTHESIS

Methodologic quality and potential for bias were assessed. The findings of 11 studies deemed to be of high or medium quality were synthesized to determine the level of evidence supporting the association between each risk factor studied and risk of injury during basic combat training. Quality assessment and evidence synthesis were performed from June to September 2013.

CONCLUSIONS

There is strong or moderate evidence supporting association of older age, history of smoking, and self-rated low physical activity level prior to basic combat training with increased risk of training-related injury among male trainees. There is limited, mixed, or insufficient evidence to identify risk factors for injury among female trainees.